Spring-oriented rotary shear key for use in a mold

ABSTRACT

A spring-oriented rotary shear key is used in a mold for forming a container with a latch opening, from a sheet of deformable material. The mold has upper and lower mold portions with die surfaces disposed facing each other and configured to press the sheet of deformable material inserted therebetween into a container. Upper and lower keys, each having a shear surface, are mounted in the upper and lower mold portions, respectively, such that the shear surfaces face each other in substantially parallel alignment to form an opening in the container as the mold portions travel towards each other. The lower key is mounted such that its shear surface rotates along an axis normal to a path of travel of the mold portions.

FIELD OF THE INVENTION

The present invention relates generally to a mold used for forming acontainer with a latch opening, from a deformable material. Morespecifically, the present invention relates to a spring-oriented rotaryshear key for use in such a mold.

BACKGROUND OF THE INVENTION

Molded plastic containers, more specifically, containers molded fromexpanded organic polymer material, are available in different shapes andsizes for packaging a variety of fragile articles, such as eggs, lightbulbs and the like. Such containers are particularly useful to protectthe fragile articles from impact, changes in temperature and otheradverse environmental effects.

The technique for forming such containers, well known in the industry,involves heating a wide, continuous sheet of plastic material to softenit for molding. The softened sheet is then advanced repeatedly inbetween the upper and lower portions of multi-cavity molds and the moldportions are pressed together against the softened sheet to form thecontainers. When pressed together, the mold portions are cooled to fixthe plastic in its molded shape. The mold portions are then separatedand the process is repeated a number of times.

A majority of the containers have a cover that latches over a baseportion of the container. Such containers utilize latching arrangementswhich must withstand rough and rapid handling, or repeated opening andclosing. A simple yet effective latching arrangement is obtained byproviding a latch, extending outwardly from or adjacent to one edge ofeither the cover or base portion, which is insertable into an openingprovided in the other portion. The latch can be a flat tab, a roundprotuberance or the like.

In early methods, latch openings were formed in a separate punchingprocess after the cartons were molded. This separate process requiredadditional equipment and labor, thereby increasing the cost ofmanufacturing such containers.

Subsequent methods, such as described in U.S. Pat. No. 3,845,187,eliminate the separate punching process. The latch opening is formedduring the molding process itself. As the mold portions close, thesoftened sheet of plastic is stretched over a die surface on one of themold portions, and a hole former carried by the other mold portion ispressed into contact with the die surface to cut through the plasticalong one edge of the latch opening. As the mold portions close further,resilient means are used to cause the hole former to scrape along thedie surface and push the plastic across a scraped region, away from thecut, to form a compressed wall of plastic spaced from the cut to formthe latch opening. However, the requirement that the hole former be incontact with the die surface, when it cuts through the plastic sheet,necessitates periodic sharpening or replacement of its dulled or bluntedcutting edge.

Another method utilizes a heavy spring top-loaded onto a rotary shearkey to obliquely bias the key surface and resist the horizontal vectorof the downward travel of the hole former upon this surface. Again, thisresults in a considerable scraping action between the hole former andthe key surface and misalignment of the key.

SUMMARY OF THE INVENTION

The present invention also uses a spring with a rotary shear key but thespring is lightly loaded onto the rotary shear key, preferably at thebottom, to simply orient the rotary shear key. The rotary shear key isused in a mold that has upper and lower mold portions with die surfacesdisposed facing each other and configured to press the sheet ofdeformable material therebetween into a container. An upper shear keyand a lower rotary key, each having a shear surface, are mounted in theupper and lower mold portions, respectively, such that the shearsurfaces face each other to form an opening in the container as the moldportions are pressed together.

In accordance with a preferred embodiment of the present invention, thelower rotary key is configured to closely contact the upper shear key,without causing breakage of the keys as a result of misalignment, and toreduce wear of the shear surfaces. The lower rotary key of the presentinvention completely and neatly removes the deformable material at thelocation where the latch opening is formed. The lower rotary key ismounted such that its shear surface rotates on an axis normal to thepath of travel of the mold portions.

More particularly, the lower rotary key pivotally rotates up and downabout a pivot pin extending horizontally therethrough. The upper shearkey travels downwardly and engages a chamfer on the top edge of a lowerrotary key, causing the lower rotary key to rotate around the pivot pinso that the upper shear key travelling vertically downwardly can clearand thereafter realign with the confronting surface of the lower shearkey. The lower rotary key is oriented, i.e., positioned substantiallyvertically by the spring which allows the lower rotary key to return toits original position and realign itself.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention is illustrated in and bythe following drawings in which like reference numerals indicate likeparts and in which:

FIG. 1 is a perspective view, partially cut away, showing a lower moldportion of a mold for forming an egg carton incorporating aspring-oriented rotary shear key of the present invention;

FIG. 2 is a cross-sectional view of a portion of FIG. 1, taken alongline 2--2, showing a spring disposed in a cavity of the lower rotary keyand of a portion of an upper shear key; and

FIG. 3 is an exploded view, of a portion of the lower rotary key of FIG.1, illustrating the assembly thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates generally a mold 10 for forming a container, such asan egg carton (of similar configuration as the exemplary moldillustrated in FIG. 1) with a latch opening (not shown). The mold 10incorporates a spring-oriented rotary shear key in accordance with apreferred embodiment of the present invention which is configured toclosely contact the upper shear key (in substantially parallelalignment) to form the latch opening, without causing breakage of thekeys as a result of misalignment, and to reduce wear of the shearsurfaces of the upper and lower keys. The lower rotary key of thepresent invention completely and neatly removes the deformable materialat the location where the latch opening is formed.

Typically, the mold 10 includes upper and lower mold portions formedwith facing die surfaces. The facing die surfaces are suitably shaped tocontour a sheet of deformable material inserted therebetween into theform of a container. Not shown, but well known to those skilled in theart, are means for supporting the mold portions, spaced apart from oneanother by a distance sufficient to permit the insertion of the sheet ofdeformable material, and means for pressing the mold portions toward oneanother along a vertical path of travel to form the container.

In particular, a lower portion 12 of the mold illustrated in FIG. 1forms thermoplastic egg cartons with two latch openings in the lid ofthe cartons, at locations corresponding to the two spring-orientedrotary shear keys shown. The lower portion 12 is identical to aplurality of such portions in a bank of mold stations in a tandemarrangement. The mold stations are arranged to simultaneously form aplurality of containers between their facing surfaces. The containersare molded from a sheet of deformable material, such as organic polymermaterial, preferably an expanded organic polymer material, such asexpanded polystyrene. The choice of a particular deformable materialdepends, in part, on the type of articles to be enclosed in thecontainer.

The lower portion 12 has a lower rotary key 14 of the spring-orientedrotary shear key of the present invention mounted thereto. Acorresponding upper portion (not shown) of the mold 10 presses againstthe lower portion 12, compressing the deformable material therebetweento form the container. The invention is illustrated with verticallyshearing keys (keys having shear surfaces located in a plane parallel tothe plane of the closing motion of the mold portions), but the inventionalso has application to obliquely disposed keys. The embodimentdisclosed herein merely exemplifies the invention which may take formsthat are different from the specific embodiment disclosed.

The lower portion 12 of the mold 10 comprises a base portion 18, havinga plurality of depressions 20 to form the base of an egg carton, and acover 22 to form the cover of the egg carton. Preferably, lower rotarykey 14 and the upper shear key 34 are mounted at suitable locations onthe mold where latch openings are desired. In the illustratedembodiment, the lower rotary key 12 is secured at one end 23 of thecover 22 to shear away a portion of the sheet of deformable material toform a latch opening, and an identical one is secured at another end 25.The lower rotary key 14 is secured to the lower mold portion 12 by bolts24, which are received through threaded openings 29 in the lower moldportion 12 and through threaded holes 26 formed in the lower rotary key14. Pins 30 extending from the lower mold portion 12 are press fit intocorresponding bores 32 in the lower rotary key 14.

Referring now to FIG. 2, there is shown a portion of an upper shear key34 and the lower mold portion 12. The upper shear key 34 affixed to anupper mold portion (not shown) has a flat shear surface 36, located in aplane parallel to the closing motion of the upper mold portion againstthe lower mold portion 12.

The lower rotary key 14 fits into a complimentary hollow chamber 38formed within the lower mold portion 12. The dimensions of the hollowchamber 38 are such that the lower rotary key 14 is free to pivotallyrotate within a predetermined range of angles.

The lower key 14 has a flat shear surface 40, located in a planeparallel to the plane of the closing motion of the mold. At the top ofthe shear surface 40 is a chamfered edge 42 which forms a leading edgeextending and adjacent the width of the latch opening, as best shown inFIG. 3.

Referring now to FIGS. 2 and 3, the support 28 comprises a centrallylocated depression 46 having parallel guiding members 48 disposed oneither side thereof. The lower rotary key 14 is received within thedepression 46 between the guiding members 48 and has a bore 50 extendingtherethrough aligned with corresponding bores 52 formed in the parallelguiding members 48. A pivot pin 54 is received through bores 50 and 52to pivotally mount the lower rotary key 14 to the support 28.

As best shown in FIG. 2, at an end 56, remote from the pin 54, the lowerrotary key 14 has an upper half 58 of a cavity 60 formed therein alignedwith a lower half 62 of the cavity 60 formed in the support 28. Thecavity 60 extends along a vertical axis and is preferably cylindrical. Aspring 64, preferably a coil spring, is disposed within the cavity 60such that it contacts inner end surfaces 61 of the cavity 60.

The lower rotary key 14 rotates, or pivots up and down about the pin 54.The range of angles about which the lower rotary key 14 pivotallyrotates is limited by an upper wall 66 of the chamber 38 and a surface68 of the support 28. The spring 64 orients the lower rotary key 14 suchthat the lower rotary key 14 returns to its original position afterrotating therefrom. The spring 64 preferably has a tension sufficient toensure that the lower rotary key 14 returns to its original position andto cause the shear faces 40 and 36 to realign themselves.

During the molding operation, the upper shear key 34 travels downwardly,indicated by the arrow shown in FIG. 2, and engages the chamfer 42,causing the lower rotary key 14 to pivotally rotate around the pin 4 sothat the upper shear key 34, travelling vertically downwardly can clearand thereafter realign itself with the shear surface 40 of the lowershear key 14. The shear surfaces 36 and 40 are spaced apart from oneanother by a distance which is less than the width of the sheet of thedeformable material which facilitates slidable contact of the shearsurfaces 36 and 40.

The lower rotary key 14 advantageously facilitates ease of assembly anddisassembly should a part wear out or become damaged. The lower rotarykey 14 allows the orientation of the shear surfaces 36 and 40 to be morereadily aligned and stay aligned for longer periods of time.Consequently, the accuracy of the formation of the latch opening isincreased and the frequency required for sharpening or replacing thekeys is substantially reduced in contrast to prior keys.

Although the invention has been described in terms of a preferredembodiment thereof, other embodiments that are apparent to those ofordinary skill in the art are also within the scope of the invention.Accordingly, the scope of the invention is intended to be defined onlyby reference to the appended claims.

What is claimed is:
 1. A rotary shear key for use in a mold having upperand lower mold portions that move along a path of travel, for forming alatch opening in a deformable sheet, comprising:a lower key oriented bya spring and mounted to the lower mold portion, having a shear surfacealong which the latch opening is formed; and means for rotating saidshear surface about an axis normal to the path of travel of the upperand lower mold portions, comprising a pivot pin extending along saidaxis normal to the path of travel.
 2. A rotary shear key for use in amold as defined in claim 1, further comprising:an upper shear keymounted to the upper mold portion and configured to engage a leadingsurface of said lower key and cause said lower key to pivotally rotateabout said axis.
 3. A rotary shear key for use in a mold as defined inclaim 2, wherein said leading surface is chamfered.
 4. A rotary shearkey for use in a mold as defined in claim 2, wherein said upper shearkey has a second shear surface disposed in parallel alignment with saidfirst shear surface, said second shear surface slidably engaging saidshear surface of said lower key.
 5. A rotary shear key for use in a moldas defined in claim 4, wherein said second shear surface is orientedalong an axis parallel to the path of travel.
 6. A rotary shear key foruse in a mold as defined in claim 1, wherein said lower key is pivotallysecured to a support mounted to the lower mold portion.
 7. A rotaryshear key for use in a mold for forming a container with a latchopening, from a sheet of deformable material, the mold having upper andlower mold portions configured to travel toward each other along a pathof travel and close against the sheet, comprising:an upper shear keyhaving a first shear surface, said upper shear key mounted to the uppermold portion; a lower rotary key oriented by a spring and mounted to thelower mold portion, said lower rotary key having a second shear surface,said first and second shear surfaces disposed facing each other inslidable contact to form the latch opening as the upper and lower moldportions close against the sheet; and means for pivotally rotating saidlower rotary key, said upper shear key configured to engage a surface ofsaid lower rotary key and cause said lower rotary key to pivotallyrotate about an axis normal to the path of travel, comprising a pivotpin extending along said axis normal to the path of travel.
 8. A rotaryshear key for use in a mold for forming a container with a latchopening, as defined in claim 7, wherein the shear surface of said upperkey is parallel to the path of travel to form the latch opening.
 9. Arotary shear key for use in a mold for forming a container with a latchopening, as defined in claim 7, wherein said second shear surface has aleading edge extending and adjacent the width of the latch opening. 10.A rotary shear key for use in a mold for forming a container with alatch opening, as defined in claim 7, wherein said leading edge ischamfered.
 11. A rotary shear key for use in a mold as defined in claim7, wherein said spring is disposed within a cavity located at the bottomof said lower key.
 12. A rotary shear key for use in a mold as definedin claim 7, wherein said lower key is pivotally secured to a supportmounted to the lower mold portion.
 13. A rotary shear key for use in amold having upper and lower mold portions that move along a path oftravel, for forming a latch opening in a deformable sheet, comprising:alower key mounted to the lower mold portion, having a shear surfacealong which the latch opening is formed; and means for rotating saidshear surface about an axis normal to the path of travel of the upperand lower mold portions, comprising a pivot pin extending along saidaxis normal to the path of travel.
 14. A rotary shear key for use in amold for forming a container with a latch opening, from a sheet ofdeformable material, the mold having upper and lower mold portionsconfigured to travel toward each other along a path of travel and closeagainst the sheet, comprising:an upper shear key having a first shearsurface, said upper shear key mounted to the upper mold portion; a lowerrotary key mounted to the lower mold portion, said lower rotary keyhaving a second shear surface, said first an second shear surfacesdisposed facing each other in slidable contact to form the latch openingas the upper and lower mold portions close against the sheet; and meansfor pivotally rotating said lower rotary key, said upper shear keyconfigured to engage a surface of said lower rotary key and cause saidlower rotary key to pivotally rotate about an axis normal to the path oftravel, comprising a pivot pin extending along said axis normal to thepath of travel.